A patient reports to teh endocrinology unit with very low pl

A patient reports to teh endocrinology unit with very low plasma levels of TSH, total T4, and free T3. Based on your knowledge of the link between the hypothalamus, pituitary, and thyroid glands, where do you think the defect lies?

Solution

The Hypothalamus, Pituitary and the thyroid all play a part in the feedback and regulatory mechanism involved in the production of Thyroxine (T4) and Tri-iodothyronine (T3) from the Thyroid gland.   

TRH-Thyrotropin releasing Hormone is secreted bythe Hypothalamus and stimulates the production of the polypeptide Thyroid Stimulating Hormone (TSH) from the anterior pituitary.

TSH then stimulates the production and release of T4 and T3 from the Thyroid.

Once released, T3 and T4 exerts a negative feedback mechanism on the TSH production.

T4 is the main hormone produced by the Thyroid.

T3 is mainly produced by the peripheral conversion of T4.

T3 and T4 are largely protein bound in the plasma,mainly to the Thyroxine binding Globulin-TBG. Only the unbound, or free portion is active (FT3 and FT4).

They both act via nuclear receptors to increase cell metabolism.

In the above case, the Pituitary is involved in the formation of Thyroid disease.

The patient might have had a recent treatment for Hyperthyroidism.

Congenital deficiency of TSH or TRH.